The present invention relates generally to a drive for a vehicle and more particularly to an automotive vehicle having a travelling gear including wheels or articulated treads or tracks.
In prior art vehicles of the type to which the present invention is directed, the travelling gear was driven by a drive unit via a hydraulic gearing arrangement. Usually, there was provided at least one hydraulic gear for each side of the travelling gear. The multiplication factor for one side of the travelling gear was adjustable for both the functions of driving and steering. The multiplication factor for one side of the travelling gear was independent of the multiplication factor of the other side of the travelling gear.
Vehicle drives of the aforementioned type are, in particular, used in special vehicles, such as snow clearing machines, runway maintenance vehicles, military vehicles and those used in the building or construction industry and the like. In the prior art, the transmission of power from the drive unit to the travelling gear was frequently accomplished by means of a hydraulic gearing arrangement. Associated with each side of the travelling gear was at least one hydraulic gear, for example of the type described in U.S. Pat. No. 4,116,292. The prior art arrangement made it possible to increase or decrease the vehicle driving speed when a simultaneous and identical change to the multiplication factor was made to both travelling gear sides. However, for steering, the multiplication factor of the hydraulic gears were modified in the opposite way leading to unequal speeds on the two vehicle sides. This resulted in a steering movement being initiated. In the case of articulated or full-track vehicles this type of steering arrangement was generally adopted. However, it was also used for wheeled vehicles having no special steering shaft with steering wheels.
In its simplest construction, the hydraulic gearing arrangement of the prior art had two hydraulic gears, one for each vehicle side. The prior art hydraulic gearing arrangement included a hydraulic pump, a hydraulic motor and all necessary auxiliary units, such as a feed pump, an oil container, an oil filter, etc.
It is known from the prior art to drive two hydraulic pumps and feed pumps with a drive unit that is generally a thermal motor having a toothed gearing, which is constructed as a distribution gear and which has two or three output shafts. However, this solution is not advantageous because a distribution gear constructed as toothed gearing loses power and this power loss can amount to several per cent per pair of gears.
When the distribution gear constructed as toothed gearing is fixed to the drive unit and the drive unit is itself resiliently or elastically mounted, dimensional changes occur between the hydraulic pump and the hydraulic motor. The change of spacing between the pump and the motor does not permit the use of fixed lines such as steel pipe lines. While high pressure hoses which are able to withstand the pressures occurring in such hydraulic gears are known in the prior art, the operational reliability of such hose lines is much lower than that of fixed metal pipe lines.